For 2015, the company projected per-share earnings of 27 cents to 28 cents, which compares favorably to the average estimate of 27 cents by analysts polled by Thomson Reuters.

Chief Executive Aylwin Lewis said in prepared remarks Tuesday that the company's board gave its approval for Potbelly to expand into California as a franchise-only strategy over time. Potbelly, though, didn't provide further details.

The company's strategy to spur growth include plans to expand to 1,000 restaurants in North America eventually, as well as increase the number of drive-through lanes and the portion of franchised restaurants.

The Chicago-based sandwich shop chain is part of the so-called "fast casual" or "quick-serve" niche, which features the likes of Chipotle Mexican Grill Inc.

Comparable-store sales, which includes company-operated stores open at least 15 months, increased 3.7%. Analysts expected an increase of 2.8%, according to FactSet.

Overall, Potbelly reported a profit of $1.4 million, or five cents a share, down from $1.9 million, or six cents a share, a year earlier. Excluding asset write-downs and other items, per-share earnings fell to eight cents from nine cents. Revenue increased 13% to $96 million.

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